1. Field of the Invention
The invention relates to a method for the conversion of renewable oils (triacylglycerides or TAGs) to hydrocarbons. The oils may be derived from plants, animals, or algae or mixtures thereof. The method is applicable to the manufacture of liquid transportation fuels, especially gasoline, kerosene, and jet and diesel fuels.
2. Background of the Invention
Increasing costs for petroleum-derived fuels are driving interest in alternative feedstocks. Additionally, concern over increasing atmospheric carbon dioxide levels has spawned interest in “carbon-neutral” fuels. One possible solution to both of these issues is the utilization of TAG feedstocks for the production of hydrocarbon-based transportation fuels.
Certain TAGs are already utilized as feedstocks for the production of “bio-diesel.” In this process, the TAG is transesterified with methanol to provide a fatty acid methyl ester (FAME) and glycerine. The FAME is separated, purified, and sold as an additive, supplementing petroleum-derived diesel fuel. FAME diesel additives provide certain specific benefits to their use (i.e., lubricity), but suffer serious physical limitations when used as the sole fuel and not as a blendstock (i.e., cold-flow properties).
FAME diesel fuel represents a first-generation bio-derived fuel. The shortcomings of this generation of fuel are directly related to the fuel-possessing oxygen functionality. A second-generation fuel possesses no oxygen functionality, providing a more petroleum-like product with respect to elemental composition, and is oftentimes termed “renewable diesel.”
Both Natural Resources Canada and Fortum Oil (now known as Neste Oil) have described processes and methods for the conversion of renewable feedstocks to diesel fuel. Although these second-generation fuel processes remove oxygen functionality of the fuel, these hydrodeoxygenation processes do not control the amount of even- and odd-numbered hydrocarbon chains.
Canadian Patent 2,149,685 (Natural Resources Canada) describes the conversion of depitched tall oil to a diesel fuel additive. The patent describes a hydrodeoxygenation process utilizing a hydrotreating catalyst. The catalyst is activated by presulfiding. The sulfided nature of the catalyst may be maintained by adding sulfur to the tall oil feedstock at a level of 1000 ppm. The doping agent is carbon disulfide. The hydrodeoxygenation conversion is then performed at 410° C. and 1200 psi.
United States patent application 2007/0010682 (Neste Oil) describes the preparation of a diesel fuel from a vegetable TAG oil. The TAG oil is doped with 50 to 20,000 ppm sulfur. The hydrodeoxygenation step is performed between 580 psi and 725 psi and 305° C. and 360° C.
Accordingly, there is a need for a method of producing paraffinic hydrocarbons from a feedstock comprising TAGs without the need for presulfiding the hydrotreating catalyst or doping the feedstock with sulfur. In addition, there is a need for a hydrotreating process where the resulting hydrocarbon chain lengths are distributed similarly as in conventional petroleum-derived fuels.